研究者詳細 - 丹羽　健

論文 - 丹羽　健

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新規モリブデン–窒素化合物の超高圧合成と窒素ダイマーによる軸圧縮異方性査読有り

佐々木拓也, 浅野秀斗, 丹羽健, 長谷川正

高圧力の科学と技術 33 巻 ( 4 ) 2024年

新規モリブデン–窒素化合物の超高圧合成と窒素ダイマーによる軸圧縮異方性査読有り

佐々木拓也, 浅野秀斗, 丹羽健, 長谷川正

高圧力の科学と技術 33 巻 ( 4 ) 2024年

High-pressure synthesis and low-temperature thermal expansion behavior of homogeneous phosphorus-rich pseudo-binary compound (V0.5Cr0.5)P4 査読有り

Chang, CC; Sasaki, T; Gaida, NA; Niwa, K; Hasegawa, M

CERAMICS INTERNATIONAL 49 巻 ( 24 ) 頁： 40990 - 40994 2023年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

A black phosphorus layered homogeneous phosphorus-rich compound – (V0.5Cr0.5)P4 is synthesized using a large volume press under conditions of P = 5 GPa, 1100 °C, and 1 h of heating. (V0.5Cr0.5)P4 has a monoclinic (C2/c) structure with lattice parameters and cell volume of a = 5.2307(3)Å, b = 10.861(4)Å, c = 5.8253(4)Å, β = 110.784°, and V = 309.41(4)Å3, respectively. The thermal expansion behavior above about 110K has been investigated by low-temperature synchrotron XRD. The coefficient of thermal expansion, α, was calculated to be αa = 0.57 × 10−5K−1, αb = 0.70 × 10−5K−1, αc = 0.92 × 10−5K−1, αβ = 0.13 × 10−5K−1 and αv = 2.10 × 10−5K−1 at 293K. This thermal expansion behavior presents an anisotropic expansion characteristic different from pure black phosphorus due to the V/Cr atom that bonded the black phosphorus layers together.

DOI： 10.1016/j.ceramint.2023.09.176

Thermal expansion behavior of vanadium pernitride, CuAl2-type VN2, synthesized under high pressures 査読有り

Asano, S; Niwa, K; Sasaki, T; Hasegawa, M

PROGRESS IN SOLID STATE CHEMISTRY 72 巻 2023年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress in Solid State Chemistry

CuAl2-type VN2, which is synthesized under high pressure, is a recoverable material at ambient conditions and has a high bulk modulus. In this study, we investigated the thermal expansion behavior of CuAl2-type VN2 by low-temperature X-ray diffraction measurements between 109.3(5) K and 298.3(8) K. The axial thermal expansion coefficient of VN2 was determined to be αa = 2.7(9) × 10−6 K−1 and αc = 17.8(12) × 10−6 K−1 at 298.3(8) K, which has large anisotropy similar to that of compression behavior. It is found that the small coefficient of thermal expansion of the a-axis is due to the negative and positive effects on the a-axis length with increasing temperature of the bond angles and bond lengths of VN2, respectively. As a result, VN2 exhibits very large anisotropic thermal expansion behavior.

DOI： 10.1016/j.progsolidstchem.2023.100426

High-Pressure Synthesis of a High-Pressure Phase of MnN Having NiAs-Type Structure 査読有り

Asano, S; Niwa, K; Lawler, KV; Kawaguchi-Imada, S; Sasaki, T; Hasegawa, M

INORGANIC CHEMISTRY 62 巻 ( 49 ) 頁： 20271 - 20278 2023年11月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

A novel high-pressure phase of manganese mononitride, NiAs-type MnN, was successfully synthesized through a pressure-induced phase transition from a tetragonal distorted NaCl-type MnN at pressures above approximately 55 GPa. High-pressure experiments, including starting material preparation, were conducted using a laser-heated diamond anvil cell. This result is the first example of a nitride with a structural phase transition from the distorted NaCl-type to the NiAs-type structure. Upon decompression after the phase transition to NiAs-type structure, the NiAs-type MnN underwent a structural change to the distorted NaCl-type phase, indicating the phase transition was reversible. NiAs-type MnN has a higher density and bulk modulus in comparison to the distorted NaCl-type one. The phase transition pressure of MnN is lower than that of oxides, such as FeO and MnO, which show a structural phase transition from a NaCl-type to a NiAs-type structure. It is suggested that this is due to the lattice distortion caused by antiferromagnetic ordering.

DOI： 10.1021/acs.inorgchem.3c03241

新規な14族元素窒化物の超高圧高温合成と結晶化学

丹羽健, 佐々木拓也, 長谷川正

日本結晶学会誌 65 巻 ( Supplement ) 頁： s31 - s31 2023年10月

Synthesis of garnet-type Mn4+-activated Y3(Al,Ga)5O12 and (Y,Gd)3Al5O12 phosphors with controlled emission by cation substitution 査読有り

Sasaki, T; Asaka, R; Niwa, K; Gaida, NA; Hasegawa, M

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 131 巻 ( 10 ) 頁： 696 - 700 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Ga- and Gd-substituted garnet-type Y3Al5O12:Mn4+ phosphors, Y3(Al11xGax)5O12:Mn4+ and (Y11yGdy)3Al5O12: Mn4+, were synthesized by a conventional solid-state reaction to elucidate the relationship between the emission and the local structure of the activator in the host material. Completely substituted Y3(Al11xGax)5O12 and 380 % substituted (Y11yGdy)3Al5O12 (y ¯ 30.8) solid solutions have been produced. The lattice parameters of the garnet-type solid solutions increased linearly with the substitution of Ga and Gd for Al and Y sites, respectively. The emission peak attributed to the Mn4+ luminescence center of their garnet-type solid solutions shifted toward a longer wavelength side by substituting Ga and Gd. The emission peak wavelength of the Mn4+-activated garnet-type solid solutions increased almost linearly with increasing the average bond length between the cation and anion in the dodecahedral sites. The dodecahedral site in the garnet structure is edge-sharing with the octahedral site where Mn4+ exists. These results indicate that the emission wavelength can be controlled by changing the local structure around Mn4+ due to the cation substitution of coordination polyhedra neighboring Mn4+ coordination polyhedra.

DOI： 10.2109/jcersj2.23063

Low-temperature thermal expansion behavior of the entropy-stabilized oxide (MgCoNiCuZn)O 査読有り

Chang C.C., Sasaki T., Alexander Gaida N., Niwa K., Hasegawa M.

Materials Letters 347 巻 2023年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Letters

The coefficient of thermal expansion (CTE) of entropy-stabilized oxide (MgCoNiCuZn)O has been firstly experimentally measured and studied at low temperatures below room temperature. The temperature-dependent lattice parameters of (MgCoNiCuZn)O were determined by synchrotron X-ray diffractometry. A CTE value of α = 2.2780x10-5 K−1 at 113 K for (MgCoNiCuZn)O was calculated using a second-degree polynomial fitting. The quenched homogeneous NaCl-type (MgCoNiCuZn)O structure has the highest CTE value below 133 K among all its constituent oxides. An unquenched (MgCoNiCuZn)O was also investigated, and the homogeneity was found to affect CTE values. Finally, the anisotropic behavior of the constituent oxides and (MgCoNiCuZn)O were also compared.

DOI： 10.1016/j.matlet.2023.134601

新規遷移金属多窒化物の超高圧高温合成と圧縮および熱膨張特性査読有り

長谷川正, 浅野秀斗, 張仲景, 佐々木拓也, 丹羽健

熱測定 50 巻 ( 1 ) 頁： 13 - 19 2023年1月

High-pressure synthesis and crystal structures of molybdenum nitride Mo<sub>3</sub>N<sub>5</sub> with anisotropic compressibility by a nitrogen dimer 査読有り

Sasaki, T; Yamamoto, T; Asano, S; Niwa, K; Hasegawa, M

DALTON TRANSACTIONS 52 巻 ( 2 ) 頁： 469 - 475 2023年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Dalton Transactions

A novel high-pressure molybdenum nitride phase, Mo3N5, was synthesized at above 45 GPa via a nitridation reaction of molybdenum with nitrogen under high pressure using a laser-heated diamond anvil cell. Mo3N5, having an N-N dimer and 7-coordinated Mo sites, crystallizes in an orthorhombic structure with a space group of Cmcm (No. 63) without other prototype structures. The refined lattice parameters for Mo3N5 were a = 2.86201(2) Å, b = 7.07401(6) Å, and c = 14.59687(13) Å. The DFT enthalpy calculation suggested that Mo3N5 is a high-pressure stable phase, which is also consistent with an increasing coordination number compared to ambient- and low-pressure phases. The zero-pressure bulk modulus of Mo3N5 was determined to be K0 = 328(4) GPa with K′0 = 10.1(6) by the fitting for the compression curve, which is almost consistent with the theoretical E-V curve and elastic stiffness constants. The compressibility of Mo3N5 has axial anisotropy corresponding to the N-N dimer direction in the crystal structure.

DOI： 10.1039/d2dt03433f

Ultra-High-Pressure Synthesis of Transition Metal – Nitrogen Binary Compounds

Niwa K, Asano S, Chang C.C, Sasaki T, Hasegawa M

Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 33 巻 ( 1 ) 頁： 26 - 33 2023年

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu

The recent development of high-pressure experimental techniques combined with advanced characterization and analytical methods allows us to reveal the crystal chemistry of the transition metal-nitrogen binary compounds up to the megabar pressure regime. Novel early transition metal-nitrogen compounds, VN2, Nb2N3, and MoC-type WN0.6, have been synthesized by using a laser-heated diamond-anvil cell or DIA-type high-pressure apparatus. In addition to conventional high-pressure in-situ X-ray diffraction measurements, the low-temperature thermal expansion behavior and the valance state of transition metal ions of these newly synthesized compounds were revealed. In this article, the details of our experiments, and recent progress in high-pressure synthesis and crystal chemistry of transition metal-nitrogen binary compounds are reviewed.

DOI： 10.4131/jshpreview.33.26

High-pressure polycrystalline thin-film synthesis and semiconducting property of platinum pernitride 査読有り

Niwa, K; Iizuka, T; Kurosawa, M; Nakamura, Y; Valencia, HO; Kishida, H; Nakatsuka, O; Sasaki, T; Gaida, NA; Hasegawa, M

AIP ADVANCES 12 巻 ( 5 ) 頁： 055318 - 055318 2022年5月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Advances

A polycrystalline platinum pernitride (PtN2) thin-film was successfully synthesized via nitridation of a platinum thin-film deposited on α-Al2O3 substrate at the pressure of ∼50 GPa by using the laser-heated diamond anvil cell. The current-voltage characteristic and optical reflectance of the synthesized PtN2 thin-film were measured under ambient conditions. Combined with first-principles calculations, these experimental results have revealed that PtN2 exhibits semiconducting property with a bandgap of ∼2 eV. This high-pressure thin-film synthesis technique could also be applied for revealing the physical properties of other novel pernitrides synthesized under ultra-high pressure, which can offer new insights into the physical properties and functionality of the pernitrides and related nitrides.

DOI： 10.1063/5.0090089

Synchrotron-Radiation Infrared Microspectroscopy of Marcasite-Type NiN<sub>2</sub> 査読有り

Soda, K; Kawada, T; Niwa, K; Hasegawa, M; Ikemoto, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 91 巻 ( 4 ) 2022年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

The electronic structure of the marcasite-type NiN2, newly synthesized under high pressures and high temperatures, was investigated using synchrotron-radiation infrared (IR) microspectroscopy and first-principles calculations based on the density functional theory (DFT). The IR spectrum of the marcasite-type NiN2 showed characteristic low reflectance of the semiconductor with spectral features probably due to defects or lattice vibrations and free carriers. The effective free-carrier concentration in the marcasite-type NiN2 was estimated by fitting a Drude-Lorentz model for the optical response to be 1024-25 m-3, much less than those of normal metals (1028-29 m-3) and comparable to the estimated concentration of the thermally-excited carrier in the conduction band. The DFT predictions could semi-quantitatively explain the experimental findings; at 36 GPa, the marcasite-type NiN2 had a narrow gap between the Ni 3d aσ bands split in the distorted octahedral coordination of N neighbors.

DOI： 10.7566/JPSJ.91.044702

High pressure synthesis and the valence state of vanadium ions for the novel transition metal pernitride, CuAl<sub>2</sub>-type VN<sub>2</sub> 査読有り

Asano, S; Niwa, K; Sasaki, T; Gaida, NA; Hasegawa, M

DALTON TRANSACTIONS 51 巻 ( 7 ) 頁： 2656 - 2659 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Dalton Transactions

A novel transition metal pernitride, CuAl2-type VN2, has been synthesized at a pressure above 73.3 GPa. The bulk modulus has been determined to be K0 = 347(12) GPa. By hard X-ray absorption spectrum measurements of VN2, the valence state of transition metal ions in pernitrides has been for the first time experimentally reported.

DOI： 10.1039/d1dt04310b

超高圧力下での新物質・新結晶の溶液結晶成長査読有り

長谷川正, 佐々木拓也, Nico A. GAIDA, 丹羽健

日本結晶成長学会誌 49 巻 ( 2 ) 頁： n/a 2022年

Pressure-Tunable Crystal Structure and Magnetic Transition Temperature of the Nowotny Chimney-Ladder CrGeγ Phase 査読有り

Sasaki, T; Noda, K; Gaida, NA; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY 60 巻 ( 19 ) 頁： 14525 - 14529 2021年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

A Nowotny chimney-ladder (NCL) chromium germanide (CrGeγ) with varying compositions has been synthesized under high pressure. Crystal structure parameters of the NCL CrGeγ have been calculated by Le Bail refinement based on the superspace group. The refined γof CrGeγ increases with the synthesis pressure, indicating an increasing Ge content. The NCL CrGeγ phases are ferromagnetic at T = 2 K regardless of their composition, and the magnetic transition temperature (TC) increases when the γbecomes higher. It is noteworthy that CrGe1.763 and CrGe1.774 synthesized at P = 10 and 14 GPa have magnetic transition temperatures of T = 295 and 333 K above room temperature, respectively. Surprisingly, the magnetic transition temperature has changed by δTC = 270 K, although the γvalues of the raw material and the sample synthesized at P = 14 GPa differ by only δγ= 0.05, corresponding to an atomic concentration of 0.62 atom %. The synthesis pressure acts as an essential parameter in tuning the composition of the NCL phase. Accordingly, the high-pressure synthesis may significantly control several physical characteristics of NCL phases by utilizing compositional and structural modulation.

DOI： 10.1021/acs.inorgchem.1c01887

Crystal and Electronic Structure of U<sub>7</sub>Te<sub>12</sub>-Type Tungsten Nitride Synthesized under High Pressure 査読有り

Chang, CC; Sasaki, T; Gaida, NA; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY 60 巻 ( 17 ) 頁： 13278 - 13283 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Tungsten nitride continues to drive fundamental interests because of its potential as a functional compound, which combines features such as high hardness together with thermal, chemical, and wear resistance. Here, we report a novel tungsten nitride phase synthesized from MoC-type WN0.6 and molecular nitrogen after laser irradiation at P = 70 GPa in a diamond anvil cell. This novel phase is quenchable at ambient pressure and determined to be U7Te12-type tungsten nitride and crystallizes in the hexagonal space group (P6) having lattice parameters of a = 8.2398(3) Å, c = 2.94948(14) Å, and V = 173.423(13) Å3. Tungsten atoms are coordinated to eight and nine nitrogen atoms, higher than previously reported tungsten nitrides. The bulk modulus is determined to be K0 = 312 (5) GPa (K0′ = 4.0 fixed), and DFT calculations predict that U7Te12-type W7N12 has a metallic nature.

DOI： 10.1021/acs.inorgchem.1c01633

Nitriding synthesis and structural change of phosphorus nitrides at high pressures 査読有り

Niwa, K; Iijima, Y; Ukita, M; Toda, R; Toyoura, K; Sasaki, T; Matsunaga, K; Gaida, NA; Hasegawa, M

JOURNAL OF RAMAN SPECTROSCOPY 52 巻 ( 5 ) 頁： 1064 - 1072 2021年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Raman Spectroscopy

The phase stability of γ-P3N5 and the possible formation of new phosphorus nitrides were investigated via high-pressure in situ Raman spectroscopy, X-ray diffraction measurements, and first-principles calculations up to approximately 80 GPa. In this study, γ-P3N5 was synthesized via the direct nitridation of black phosphorus at a pressure approximately above 12 GPa. The Raman spectrum, bulk modulus (K0 = 130.27(43) GPa), and compression behaviors (order of axial compressibility: βc > βa > βb) were experimentally measured for the first time. These experimental results were in good agreement with those of first-principles calculations. Our high-pressure in situ measurements and first-principles calculations revealed that γ-P3N5 persisted up to 80 GPa at room temperature. The compression of γ-P3N5 proceeded with the folding of the layer consisting of the corner- and edge-sharing PN4 and PN5. The present findings indicate that the P–N bonding with a low coordination number (PN4 and PN5) is preferable and stabilized for phosphorus nitride over a wide pressure range. However, laser heating between 67 and 70 GPa in the presence of nitrogen resulted in the formation of new PxNy, which included the possibility of a new high-pressure P3N5 phase. The Raman scattering measurements along with the decompression demonstrated that the local structure of the newly synthesized PxNy metastably persisted at atmospheric pressure. The present experimental and theoretical studies on phosphorus nitrides offer new insights into the high-pressure behaviors of covalent compounds consisting of highly coordinated polyhedra.

DOI： 10.1002/jrs.6079

Electronic Structures of Transition-Metal Pernitrides Studied Using X-ray Absorption and Photoelectron Spectroscopy 査読有り

Soda Kazuo, Kato Daiki, Komabuchi Mai, Terabe Toshiki, Takayama Shin, Ibaragi Toshiki, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Takakura Shoichi, Nakatake Masashi

Journal of the Physical Society of Japan 90 巻 ( 4 ) 頁： 44710 - 44710 2021年4月

Electronic Structures of Transition-Metal Pernitrides Studied Using X-ray Absorption and Photoelectron Spectroscopy 査読有り

Soda Kazuo, Kato Daiki, Komabuchi Mai, Terabe Toshiki, Takayama Shin, Ibaragi Toshiki, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Takakura Shoichi, Nakatake Masashi

Journal of the Physical Society of Japan 90 巻 ( 4 ) 頁： 44710 - 44710 2021年4月

Phase relations and thermoelasticity of magnesium silicide at high pressure and temperature 査読有り

Gaida, NA; Niwa, K; Sasaki, T; Hasegawa, M

JOURNAL OF CHEMICAL PHYSICS 154 巻 ( 14 ) 頁： 144701 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Chemical Physics

Within the exploration of sustainable and functional materials, narrow bandgap magnesium silicide semiconductors have gained growing interest. Intriguingly, squeezing silicides to extreme pressures and exposing them to non-ambient temperatures proves fruitful to study the structural behavior, tune the electronic structure, or discover novel phases. Herein, structural changes and thermoelastic characteristics of magnesium silicides were probed with synchrotron x-ray diffraction techniques using the laser-heated diamond anvil cell and large volume press at high pressure and temperature and temperature-dependent synchrotron powder diffraction. Probing the ambient phase of Mg2Si (anti-CaF2-type Mg2Si, space group: Fm3¯m) at static pressures of giga-Pascals possibly unveiled the transformation to metastable orthorhombic anti-PbCl2-type Mg2Si (Pnma). Interestingly, heating under pressures introduced the decomposition of Mg2Si to hexagonal Mg9Si5 (P63) and minor Mg. Using equations of state (EoS), which relate pressure to volume, the bulk moduli of anti-CaF2-type Mg2Si, anti-PbCl2-type Mg2Si, and Mg9Si5 were determined to be B0 = 47(2) GPa, B0 ≈ 72(5) GPa, and B0 = 58(3) GPa, respectively. Employing a high-temperature EoS to the P-V-T data of anti-CaF2-type Mg2Si provided its thermoelastic parameters: BT0 = 46(3) GPa, B′T0 = 6.1(8), and (∂BT0/∂T)P = -0.013(4) GPa K-1. At atmospheric pressure, anti-CaF2-type Mg2Si kept stable at T = 133-723 K, whereas Mg9Si5 transformed to anti-CaF2-type Mg2Si and Si above T ≥ 530 K. This temperature stability may indicate the potential of Mg9Si5 as a mid-temperature thermoelectric material, as suggested from previous first-principles calculations. Within this realm, thermal models were applied, yielding thermal expansion coefficients of both silicides together with estimations of their Grüneisen parameter and Debye temperature.

DOI： 10.1063/5.0044648

Crystal and Electronic Structures of MoSi<sub>2</sub>-Type CrGe<sub>2</sub> Synthesized under High Pressure 査読有り

Sasaki, T; Kanie, K; Yokoi, T; Niwa, K; Gaida, NA; Matsunaga, K; Hasegawa, M

INORGANIC CHEMISTRY 60 巻 ( 3 ) 頁： 1767 - 1772 2021年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Chromium germanides, namely, Nowotny chimney-ladder-phase CrGe1.77 and MoSi2-type CrGe2, were synthesized above 15 GPa or more via laser heating using a diamond anvil cell (LHDAC). MoSi2-type CrGe2, which is the most Ge-rich compound in the Cr-Ge system, crystallizes in the tetragonal structure with a space group of I4/mmm (no. 139) and lattice parameters of a = 3.24919(6) Å and c = 8.0523(3) Å and is isostructural with MoSi2. MoSi2-type CrGe2 has a deep pseudogap caused by the splitting of 3d orbitals with Cr, as evidenced by ab initio calculation. In this article, we have succeeded in synthesizing a binary compound between transition-metal and metalloid elements for the first time at high pressures above 10 GPa using the LHDAC. This pathway opens the possibility to explore more compounds in this system and may provide new insights into the fundamental interaction between these two elements.

DOI： 10.1021/acs.inorgchem.0c03240

Elasticity of nanocrystalline kyanite at high pressure and temperature from ultrasonic and synchrotron X-ray techniques 査読有り

Gaida, NA; Gréaux, S; Kono, Y; Ohfuji, H; Kuwahara, H; Nishiyama, N; Beermann, O; Sasaki, T; Niwa, K; Hasegawa, M

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 104 巻 ( 1 ) 頁： 635 - 644 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Ceramic Society

Material properties, such as elasticity data at wide-ranging conditions of pressure and temperature, attract increasing attention for material and earth sciences. In particular, polycrystalline ceramics for next-generation photonic applications are nowadays fabricated by advanced syntheses techniques operating under elevated pressures and temperatures. Herein, the elastic properties of a synthetic transparent and reinforced aluminosilicate nanoceramic composed of triclinic kyanite with minor amounts of trigonal α-alumina crystals are investigated using in situ synchrotron X-ray diffraction and ultrasonic techniques at high-pressure (up to 11 GPa) and high-temperature (300-1500 K) conditions. This not only enables the determination of the equation of state (EoS) parameters by applying the pressure-volume-temperature (P-V-T) data to the high-temperature Birch-Murnaghan EoS but also yields the elastic moduli together with their P and T derivatives from the fit of the compressional and shear wave velocities to a finite strain EoS: KS0,300 = 186(2) GPa, K′S0,300 = 7.2(6), (∂KS0,300/∂T)P = −0.023(2) GPa K−1, G0,300 = 125(1) GPa G′0,300 = 2.3(2), (∂G0,300/∂T)P = −0.017(1) GPa K−1. On the basis of our acquired results, we propose to predict the elastic moduli of aluminosilicate ceramics by a linear function of the ratio of AlO6 octahedra and SiO4 tetrahedra within the constituting phases.

DOI： 10.1111/jace.17464

Thermal Expansion of Incompressible U<sub>2</sub>S<sub>3</sub>-Type Nb<sub>2</sub>N<sub>3 </sub>Synthesized in a Diamond Anvil Cell

Asano, S; Niwa, K; Sasaki, T; Gaida, NA; Hasegawa, M

INORGANIC CHEMISTRY 59 巻 ( 12 ) 頁： 7915 - 7918 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

A novel niobium nitride, U2S3-type Nb2N3, has been successfully synthesized by nitridation of δ-NbN above approximately 30 GPa in a laser-heated diamond anvil cell. Nb2N3 crystallizes in the same orthorhombic structure (space group: Pnma) as η-Ta2N3. Nb2N3 consists of regular-shaped polyhedra, and the bulk modulus has been determined to K0 = 300(2) GPa. The low-temperature X-ray diffraction measurements have been successfully conducted for the tiny novel Nb2N3 between 297.7(5) and 106.3(3) K under ambient pressure. Nb2N3 shows no structural phase transition down to 106.3(3) K, and investigation of the linear thermal expansion coefficients yields αa = 3.36(9) × 10-6 K-1, αb = 5.39(10) × 10-6 K-1, αc = 6.77(15) × 10-6 K-1, respectively. Our study reveals that the incompressible novel nitride shows low thermal expansion behavior, which offers new insights for the development of functional nitrides and their crystal chemistry.

DOI： 10.1021/acs.inorgchem.0c01057

Crystal structures and electronic properties of Sn<sub>3</sub>N<sub>4</sub> polymorphs synthesized <i>via</i> high-pressure nitridation of tin

Niwa, K; Inagaki, T; Ohsuna, T; Liu, Z; Sasaki, T; Gaida, NA; Hasegawa, M

CRYSTENGCOMM 22 巻 ( 20 ) 頁： 3531 - 3538 2020年5月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：CrystEngComm

The crystal structures, compression behaviors, and electronic properties of Sn3N4 polymorphs were investigated by means of high-pressure in situ measurements, transmission electron microscopy, and DFT ab initio calculations. The direct nitridation of tin above a pressure of 29.5 GPa by using a laser-heated diamond anvil cell resulted in the synthesis of highly crystalline monoclinic Sn3N4 which so far is consistent with the reported one. On the other hand, it was newly discovered that the monoclinic Sn3N4 undergoes phase transition twice along with decompression at ambient pressure. Advanced synchrotron X-ray powder diffraction measurements and TEM analyses on the recovered sample demonstrate that the newly recovered Sn3N4 crystallizes with orthorhombic symmetry and consists of irregularly shaped SnN5 and SnN6. DFT ab initio calculations reveal that this newly recovered orthorhombic Sn3N4 is an indirect band gap semiconductor having a narrower electronic energy gap than that of cubic spinel-type Sn3N4. The present results demonstrate that high-pressure nitridation is a powerful method to synthesize highly crystalline Sn3N4 polymorphs and reveal the new crystal chemistry of group IVA nitrides with respect to the variety of crystal structures and electronic properties.

DOI： 10.1039/d0ce00210k

Hydrogen Depth-profiles in Nb Hydrides Formed in Supercritical Water 査読有り

Soda Kazuo, Sugiura Shinya, Yamaguchi Kanta, Kato Masahiko, Niwa Ken, Hasegawa Masashi, Suzuki Kohtaku, Ishigami Ryoya, Ikenaga Eiji

e-Journal of Surface Science and Nanotechnology 18 巻頁： 152-158 2020年4月

Nanowire crystals of tantalum nitride grown in ammonium halide fluxes at high pressures

Gaida, NA; Sasaki, T; Liu, Z; Niwa, K; Hirozawa, M; Ohsuna, T; Hasegawa, M

APPLIED PHYSICS LETTERS 116 巻 ( 12 ) 2020年3月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Nanowire crystals of a tantalum nitride phase have been grown from epsilon-tantalum nitride and ammonium halide precursors at high pressures exceeding several gigapascals. Synchrotron x-ray diffraction and Transmission Electron Microscopy (TEM) observations revealed that they had crystallized in an unreported hexagonal structure with lattice parameters of a = 3.050(1) Å and c = 2.909(2) Å. The one-dimensional growth orientation was along the crystallographic [001] direction. Scanning TEM-EDX elemental analyses showed that the nanowire crystals were composed of tantalum and nitrogen with small amounts of oxygen. The presence of the melted ammonium halides combined with supercritical ammonia acting as a reactive flux at high pressure and temperature played a significant role in the nanowire crystal growth. Raman spectroscopy performed on several single crystal nanowires pointed toward metallic properties, and the temperature dependence of the magnetization measured by Superconducting Quantum Interference Device magnetometry suggested a superconducting transition about 6.2 K. The analysis of the compression behavior revealed an incompressible nature, and the bulk modulus was determined to be 363(6) GPa.

DOI： 10.1063/1.5140856

Microstructural effects on hardness and optical transparency of birefringent aluminosilicate nanoceramics 査読有り

Gaida N.A, Nishiyama N, Beermann O, Schürmann U, Masuno A, Giehl C, Niwa K, Hasegawa M, Bhat S, Farla R, Kienle L

International Journal of Ceramic Engineering and Science 2 巻 ( 2 ) 頁： 76 - 82 2020年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Ceramic Engineering and Science

Transparent nanoceramics, synthesized at extreme conditions of high pressure and temperature, are new classes of materials highly attractive for photonic applications, such as optical windows, which require additional increased hardness and toughness. In this study, mechanical properties of transparent polycrystalline nanoceramics consisting of triclinic Al2SiO5 kyanite (~91.4 vol%) and trigonal Al2O3 corundum (~8.6 vol%) fabricated at high pressure (10 GPa) and temperature (1200-1400°C) were investigated. It is already known that the optical transparency of kyanite-based nanoceramics increases with decreasing average grain size. The present study shows that the hardness of these ceramics increases with decreasing grain sizes down to ~70 nm according to the Hall-Petch strengthening. This grain size seems to mark a transition range where an inverse Hall-Petch effect is indicated due to signs of a moderate hardness decrease at a smaller grain size of ~35 nm. The observed hardness-grain size relation can fairly be described by an existing composite model, which considers the crystals to be harder than the noncrystalline grain boundaries. Within the range of average grain sizes examined, the kyanite habit changes from more equant to more columnar. This behavior is associated with the observed strong crack deflection by the columnar kyanite grains with aspect (length to diameter) ratios ranging from ~2 to 10 and may positively affect the fracture toughness.

DOI： 10.1002/ces2.10036

超高圧力下での直接窒化反応による白金族金属二窒化物の創製査読有り

長谷川正, 丹羽健

応用物理 89 巻 ( 2 ) 頁： 87 - 91 2020年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人応用物理学会

<p>白金族元素（Ru，Rh，Pd，Os，Ir，Pt）は常圧下では窒素に対して不活性であり，従来は窒化物を形成しないとされてきた．ところが，数十GPa以上の超高圧下での直接窒化反応を用いると，これらの金属の二窒化物が創製される．ここでは，金属二窒化物などの金属多窒化物という新しい物質群について，現在世界で展開されている物質科学研究の一端を紹介する．最初に，ダイヤモンドアンビルセルという超高圧発生装置とレーザー加熱を組み合わせた超高圧合成技術について説明する．次に，合成された白金族金属二窒化物の安定性，結晶構造，物性について簡単に紹介する．そして最後に，白金族元素以外の金属においても創製される二窒化物の研究例として，世界で唯一初めての単結晶育成に成功したCrの二窒化物について述べる．</p>

DOI： 10.11470/oubutsu.89.2_87

High-Pressure Synthesis and Crystal Structure of MoC-Type Tungsten Nitride by Nitridation with Ammonium Chloride

Sasaki, T; Ikoma, T; Sago, K; Liu, Z; Niwa, K; Ohsuna, T; Hasegawa, M

INORGANIC CHEMISTRY 58 巻 ( 24 ) 頁： 16379 - 16386 2019年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

A novel tungsten nitride, MoC-type WN, was synthesized at 6 GPa and 1200 °C via nitridation of tungsten by ammonium chloride as a nitrogen source. This compound is isostructural with γ′-MoC, which has a hexagonal structure with a space group of P63/mmc (No. 194). Micrometer-sized single crystals of MoC-type WN were grown in molten ammonium chloride flux. In addition, NaCl-type WN and WC-type WN were synthesized via nitridation by ammonium chloride at 6 GPa and 1000 °C. Ammonium chloride is appropriate as a nitrogen source for nitride synthesis under high pressure. The new WN phase crystallizes in the hexagonal structure with unit cell parameters of a = 2.89248(2) Å and c = 10.17069(7) Å. The chemical formula of MoC-type WN refined by the Rietveld analysis from powder X-ray diffraction data was WN0.60(1). The zero-pressure bulk modulus, K0, of MoC-type WN was determined to be 338(3) GPa, which can be expected to be a hard material.

DOI： 10.1021/acs.inorgchem.9b01945

Hydrogen-Storing Salt NaCl(H<sub>2</sub>) Synthesized at High Pressure and High Temperature

Matsuoka, T; Muraoka, S; Ishikawa, T; Niwa, K; Ohta, K; Hirao, N; Kawaguchi, SI; Ohishi, Y; Shimizu, K; Sasaki, S

JOURNAL OF PHYSICAL CHEMISTRY C 123 巻 ( 41 ) 頁： 25074 - 25080 2019年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

X-ray diffraction and Raman scattering measurements, and first-principles calculations are performed to search for the formation of a NaCl-hydrogen compound. When the NaCl and H2 mixture is laser-heated to above 1500 K at pressures exceeding 40 GPa, we observe the formation of NaClHx with P63/mmc structure which accommodates H2 molecules in the interstitial sites of the NaCl lattice forming ABAC stacking. Upon the decrease of pressure at 300 K, NaClHx remains stable down to 17 GPa. Our calculations suggest the observed NaClHx is NaCl(H2). In addition, a hydrogen-richer phase NaCl(H2)4 is predicted to become stable at pressures above 40 GPa.

DOI： 10.1021/acs.jpcc.9b06639

High-Pressure Synthesis and Phase Stability of Nickel Pernitride

Niwa, K; Fukui, R; Terabe, T; Kawada, T; Kato, D; Sasaki, T; Soda, K; Hasegawa, M

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2019 巻 ( 33 ) 頁： 3753 - 3757 2019年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：European Journal of Inorganic Chemistry

The high-pressure nitridation of nickel was investigated using a laser-heated diamond-anvil cell. Marcasite-type nickel pernitride (NiN2) was synthesized at approximately 40 GPa, and it transformed into the tetragonal phase at approximately 3 GPa along with the decompression. The structural refinement of marcasite-type NiN2 at 36 GPa gives an N-N distance of 1.24 Å. The first-principles calculation reveals that the marcasite-type NiN2 is a narrow-gap semiconductor, and high-pressure in-situ X-ray diffraction measurements revealed a zero-pressure bulk modulus of 172(6) GPa. The axial ratios (c/a and b/a) of marcasite-type NiN2 are close to the upper-limit values of marcasite-type structures, which suggests that the stability of marcasite-type transition metal pernitrides strongly depends on the d-electrons.

DOI： 10.1002/ejic.201900489

Lithium ionic conductivities of α-LiBO<sub>2</sub> with two-dimensional Li-Li networks and γ-LiBO<sub>2</sub> with three-dimensional ones synthesized under high pressure 査読有り

Hirose, E; Kataoka, K; Nagata, H; Akimoto, J; Sasaki, T; Niwa, K; Hasegawa, M

JOURNAL OF SOLID STATE CHEMISTRY 274 巻頁： 100 - 104 2019年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Solid State Chemistry

Lithium ionic conductivities of two LiBO 2 polymorphs, i.e. the same composition Li borates: α-LiBO 2 and γ-LiBO 2 , which are ambient and high-pressure phases, have been measured by the AC impedance method between 450 and 520 K using their high-density polycrystalline samples synthesized under high pressures. It is found the intra-grain and total conductivities of the γ-LiBO 2 have been measured for the first time and be of the order 10 −5 ∼ 10 −6 Scm −1 and 10 −6 Scm −1 , respectively, both of which are higher in whole measured temperature range than those of the α-LiBO 2 . The higher lithium ionic conductivities of the former are discussed from the viewpoints of local structure and Li ion network in the crystal structures of the α-LiBO 2 and γ-LiBO 2 .

DOI： 10.1016/j.jssc.2019.02.045

High-pressure synthesis, crystal growth, and compression behavior of hexagonal CrN<sub>2</sub> having one-dimensionally aligned nitrogen dimer 査読有り

Niwa, K; Yamamoto, T; Sasaki, T; Hasegawa, M

PHYSICAL REVIEW MATERIALS 3 巻 ( 5 ) 2019年5月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review Materials

A hexagonal chromium pernitride, CrN2, has been successfully synthesized via a direct chemical reaction between chromium and molecular nitrogen at a pressure of approximately 70 GPa. The advanced synchrotron x-ray diffraction (XRD) measurements after recovery and structural refinement at 0.1 MPa demonstrated that CrN2 crystallizes in the anti-NiAs-type structure with lattice parameters of a=2.7465(3)Å and c=7.3670(4)Å. Micron-sized hexagonal habit compounds were found in the synthesized products, which indicated that the single crystal of hexagonal CrN2 was grown in the supercritical nitrogen at high pressure. High-pressure in situ XRD measurements were performed to determine the zero-pressure bulk modulus, K0, value of 286(6) GPa [K′0=2.5(7)] and remarkable incompressibility of the c axis. CrN2 is a unique example of the recoverable transition-metal pernitride which presents one-dimensionally aligned N-N dimers in the structure. The one-dimensionally aligned N-N dimers play an important role in controlling the mechanical and electronic properties of CrN2 as predicted by theoretical calculations.

DOI： 10.1103/PhysRevMaterials.3.053601

Infrared spectroscopy on electronic structures of platinum-group metal pernitrides <i>M</i>N<sub>2</sub> (<i>M</i> = Ru, Rh, Ir, and Pt) 査読有り

Soda, K; Komabuchi, M; Maeguchi, K; Kato, M; Terabe, T; Niwa, K; Hasegawa, M; Ikemoto, Y; Okamura, H

PHYSICA B-CONDENSED MATTER 558 巻頁： 54 - 58 2019年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physica B: Condensed Matter

The electronic structures of platinum-group metal pernitrides MN 2 (M = Ru, Rh, Ir, and Pt) were investigated via synchrotron radiation infrared spectroscopy and first-principles calculations. Measured reflectance spectra of marcasite-type RuN 2 and RhN 2 showed Drude-like responses, approaching 1 as the photon energy was decreased, whereas reflectance of arsenopyrite-type IrN 2 and pyrite-type PtN 2 became ∼0.3 in the low photon energy region with a few features. These findings agreed well with the predictions of the metallic nature of marcasite-type RuN 2 and RhN 2 and the semiconducting properties of arsenopyrite-type IrN 2 and pyrite-type PtN 2 , respectively. The measured reflectance spectra were also reasonably consistent with the calculated optical responses. The band gaps of IrN 2 and PtN 2 were estimated to be 0.8 and 2.1 eV, respectively, via first-principles calculation with a modified Becke–Johnson (MBJ) potential for the exchange potential.

DOI： 10.1016/j.physb.2019.01.017

High-Pressure Synthesis, Crystal Chemistry, and Ionic Conductivity of a Structural Polymorph of Li<sub>3</sub>BP<sub>2</sub>O<sub>8</sub> 査読有り

Hirose, E; Kataoka, K; Nagata, H; Akimoto, J; Sasaki, T; Niwa, K; Hasegawa, M

INORGANIC CHEMISTRY 57 巻 ( 24 ) 頁： 15048 - 15050 2018年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

A new structural polymorph of Li 3 BP 2 O 8 has been successfully synthesized via a solid-state reaction between Li 3 PO 4 and BPO 4 at 4 GPa and 600 °C. The high-pressure phase of Li 3 BP 2 O 8 (HP-Li 3 BP 2 O 8 ) was found to crystallize in monoclinic symmetry with the cell parameters of a = 8.57010(4) Å, b = 11.11812(5) Å, c = 5.55380(3) Å, and β = 97.7269(3)° [space group P2 1 /a (No. 14)]. HP-Li 3 BP 2 O 8 has a new crystal structure that has not been reported so far. The total ionic conductivities measured for the polycrystalline sample by alternating-currrent impedance were 3.4 × 10 -7 and 2.1 × 10 -6 S/cm at 399 and 456 K, respectively. The lithium ionic conductivity of HP-Li 3 BP 2 O 8 was higher than that of the low-pressure phase Li 3 BP 2 O 8 in the temperature range of 375-456 K. This is caused by the difference in the dimensions of the lithium arrangements between LP- and HP-Li 3 BP 2 O 8 .

DOI： 10.1021/acs.inorgchem.8b03155

Structural stability of the Li-ion conductor Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> investigated by high-pressure in-situ X-ray diffraction and Raman spectroscopy

Hirose, E; Niwa, K; Kataoka, K; Akimoto, J; Hasegawa, M

MATERIALS RESEARCH BULLETIN 107 巻頁： 361 - 365 2018年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Research Bulletin

The high-pressure behavior of Li7La3Zr2O12 (LLZO) with a garnet-related structure has been investigated for the first time by high pressure in situ X-ray diffraction measurements and Raman spectroscopy using a diamond anvil cell. It was found that the tetragonal LLZO transforms to the high-pressure cubic phase (HP-c-LLZO) at 71.8 GPa in a N2 medium and at 25.8 GPa in the absence of pressure mediums. Uniaxial compression in the absence of pressure mediums induced the phase transition at much lower pressures than in the hydrostatic case when N2 was used as the pressure medium. High pressure in situ Raman spectroscopy suggested that the Li coordination in HP-c-LLZO was different from that reported in cubic LLZO, which had been stabilized by doping Al at ambient pressure and room temperature.

DOI： 10.1016/j.materresbull.2018.07.034

Valence-Band Electronic Structures of High-Pressure-Phase PdF<sub>2</sub>-type Platinum-Group Metal Dioxides <i>M</i>O<sub>2</sub> (<i>M</i> = Ru, Rh, Ir, and Pt)

Soda, K; Kobayashi, D; Mizui, T; Kato, M; Shirako, Y; Niwa, K; Hasegawa, M; Akaogi, M; Kojitani, H; Ikenaga, E; Muro, T

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 巻 ( 4 ) 2018年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

The valence-band electronic structures of high-pressure-phase PdF2-type (HP-PdF2-type) platinum-group metal dioxides MO2 (M = Ru, Rh, Ir, and Pt) were studied by synchrotron radiation photoelectron spectroscopy and first-principles calculations. The obtained photoelectron spectra for HP-PdF2-type RuO2, RhO2, and IrO2 agree well with the calculated valence-band densities of states (DOSs) for these compounds, indicating their metallic properties, whereas the DOS of HP-PdF2-type PtO2 (calculated in the presence and absence of spin–orbit interactions) predicts that this material may be metallic or semimetallic, which is inconsistent with the electric conductivity reported to date and the charging effect observed in current photoelectron measurements. Compared with the calculated results, the valence-band spectrum of PtO2 appears to have shifted toward the high-binding-energy side and reveals a gradual intensity decrease toward the Fermi energy EF, implying a semiconductor-like electronic structure. Spin-dependent calculations predict a ferromagnetic ground state with a magnetization of 0.475 μB per formula unit for HP-PdF2-type RhO2

DOI： 10.7566/JPSJ.87.044701

High pressure in-situ synthesis and physical properties of Cr<sub>3</sub>C<sub>2</sub>-Ni cermets 国際共著

Zhai, WY; Gao, YM; Sun, L; Wang, YR; Niwa, K; Hasegawa, M

CERAMICS INTERNATIONAL 43 巻 ( 18 ) 頁： 17202 - 17205 2017年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

A novel Cr3C2-Ni cermets were successfully in-situ synthesized with Cr, C and Ni (20 wt%) mixed-powder at 1100 °C under 0–6 GPa isostatic pressure using a small-sized cubic-type multi-anvil press apparatus. High purity Cr3C2 phase was generated in the cermets. Comparing with the conventional and reactive sintering, the sintering temperature and the average grain size of Cr3C2 decreased by 200 °C and 50%, respectively. The physical properties, normalized lattice parameters and volumes of Cr3C2−20 wt%Ni cermet as a function of pressure had been studied both experimentally and by first-principles calculations for the first time.

DOI： 10.1016/j.ceramint.2017.09.145

Pyrite form of group-14 element pernitrides synthesized at high pressure and high temperature

Niwa, K; Ogasawara, H; Hasegawa, M

DALTON TRANSACTIONS 46 巻 ( 30 ) 頁： 9750 - 9754 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Dalton Transactions

The chemical reaction of group-14 elements with molecular nitrogen at pressures above 60 GPa successfully leads to the formation of pyrite-type pernitrides. These new crystalline group-14 elemental pernitrides were found to show a bulk modulus higher than the other known group-14 elemental nitrides. Our results offer significant new progress in the solid-state chemistry of nitrides.

DOI： 10.1039/c7dt01583f

Microbeam Hard X-ray Photoemission Study on Platinum-Group Metal Pernitrides

Soda, K; Mizui, T; Komabuchi, M; Kato, M; Terabe, T; Suzuki, K; Niwa, K; Shirako, Y; Hasegawa, M; Akaogi, M; Kojitani, H; Ikenaga, E

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 巻 ( 6 ) 頁： 64804 - 64804 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

Using microbeam hard X-ray photoelectron spectroscopy, we clarified the valence-band electronic structures and chemical states of platinum-group metal (Ru, Ir, and Pt) pernitrides, which have been synthesized in supercritical nitrogen fluid under extremely high pressures and temperatures. Their nitrogen contents relative to the platinum-group metal are estimated to be 2 from the photoemission intensity, which is consistent with the studies reported to date. The observed valence-band structures agree quite well with theoretically predicted structures for the pyrite-type PtN2, arsenopyrite-type IrN2, and marcasite-type RuN2. The origin of their extremely large bulk moduli is discussed based on the current results of the valence-band structures and core-level chemical shifts.

DOI： 10.7566/JPSJ.86.064804

Highly Coordinated Iron and Cobalt Nitrides Synthesized at High Pressures and High Temperatures

Niwa, K; Terabe, T; Kato, D; Takayama, S; Kato, M; Soda, K; Hasegawa, M

INORGANIC CHEMISTRY 56 巻 ( 11 ) 頁： 6410 - 6418 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Highly coordinated iron and cobalt nitrides were successfully synthesized via direct chemical reaction between a transition metal and molecular nitrogen at pressures above approximately 30 GPa using a laser-heated diamond anvil cell. The synthesized novel transition metal nitrides were found to crystallize into the NiAs-type or marcasite-type structure. NiAs-type FeN could be quenched at ambient pressure, although it was gradually converted to the ZnS-type structure after the pressure was released. On the other hand, CoN was recovered with ZnS-type structure through a phase transition from NiAs-type structure at approximately a few gigapascals during decompression. Marcasite-type CoN2 was also synthesized at pressures above approximately 30 GPa. High-pressure in situ X-ray diffraction measurement showed that the zero-pressure bulk modulus of marcasite-type CoN2 is 216(18) GPa, which is comparable to that of RhN2. This indicates that the interatomic distance of the N-N dimer in marcasite-type CoN2 is short because of weak orbital interaction between cobalt and nitrogen atoms, as in RhN2. Surprisingly, a first-principles electronic band calculation suggests that the NiAs-type FeN and CoN and marcasite-type CoN2 exhibit metallic characteristics with magnetic moments of 3.4, 0.6, and 1.2 μB, respectively. The ferromagnetic NiAs-type structure originates from the anisotropic arrangement of transition atoms stacked along the c axis.

DOI： 10.1021/acs.inorgchem.7b00516

Synthesis, crystal structure and phase transition of a Xe-N<sub>2</sub> compound at high pressure: experimental indication of orbital interaction between xenon and nitrogen

Niwa, K; Matsuzaki, F; Hasegawa, M

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 巻 ( 1 ) 頁： 59 - 63 2017年1月

High-Pressure Synthesis and Magnetic Behavior of A-Site Columnar-Ordered Double Perovskites, LnMn(Ga<sub>0.5</sub>Ti<sub>0.5</sub>)<sub>2</sub>O<sub>6</sub> (Ln = Sm, Gd)

Shimura, G; Niwa, K; Shirako, Y; Hasegawa, M

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2017 巻 ( 4 ) 頁： 835 - 839 2017年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：European Journal of Inorganic Chemistry

A-site columnar-ordered double perovskites, LnMn(Ga0.5Ti0.5)2O6(Ln = Sm, Gd), were successfully synthesized under high pressure and high temperature (6 GPa, 1375 K). From the synchrotron powder X-ray diffraction patterns, all of the diffraction peaks can be indexed by the P42/nmc space group with lattice parameters a, c ≈ 2ap(ap: primitive cubic perovskite lattice) and no ordering of the B-site cations. Rietveld analysis of the synchrotron powder X-ray diffraction patterns and Curie–Weiss fitting of their magnetizations reveal that the ionic formulae of these perovskites are Ln3+Mn2+(Ga3+0.5Ti4+0.5)2O2–6. SmMn(Ga0.5Ti0.5)2O6shows canted-antiferromagnetic behavior, whereas GdMn(Ga0.5Ti0.5)2O6exhibits two different magnetic states at low temperature depending on the applied magnetic field and shows an unusual magnetization curve. These magnetic behaviors originate by decreasing the antiferromagnetic interaction by substituting Ga3+(d10) for Ti4+(d0) and by decreasing the ferromagnetic interaction between columnar-ordered Ln3+and Mn2+.

DOI： 10.1002/ejic.201601392

Microbeam hard X-ray photoelectron and ion-beam analyses of Nb hydrides formed in supercritical water

Kazuo Soda, Shinya Sugiura, Kanta Yamaguchi, Masahiko Kato, Ken Niwa, Masashi Hasegawa, Kohtaku Suzuki, Ryoya Ishigami, Eiji Ikenaga

International Symposium on Atomic Level Characterizations for New Materials and Devices ‘17 Proceedings 2017年

Multicomponent A-site ordered perovskite BiMn3(Fe0.25Ti0.75)4O12: High-pressure synthesis, crystal chemistry and magnetic behavior 査読有り

G. Shimura, K. Niwa, Y. Shirako, S. Muto, K. Kusaba, M. Hasegawa

Solid State Communications 234-235 巻頁： 40-44 2016年

High pressure stability and ambient metastability of marcasite-type rhodium pernitride 査読有り

K. Niwa, T. Terabe, K. Suzuki, Y. Shirako, M. Hasegawa

Journal of Applied Physics 119 巻頁： 065901 2016年

Molecular routes syntheses of graphite-like C-N compounds with various N/C ratios in high pressure and temperature 査読有り

T. HORIBE, K. KUSABA, K. NIWA, M. HASEGAWA, K. YASUDA, R. ISHIGAMI

Journal of the Ceramic Society of Japan 124 巻 ( 10 ) 頁： 1013-1016 2016年

High-pressure synthesis and relationship between A-site ordering and local structure of multicomponent perovskites(Ln0.25Mn0.75) (Al0.25Ti0. 75)O3, Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Y 査読有り

G. Shimura, Y. Shirako, K. Niwa, M. Hasegawa

Journal of Solid State Chemistry 242 巻頁： 55-62 2016年

Angle-resolved hard x-ray photoemission study of Nb hydride formation in high-pressure supercritical water 査読有り

Kazuo Soda, Hiroki Kondo, Kanta Yamaguchi, Masahiko Kato, Tatsuhito Shirak, Ken Niwa, Keiji Kusaba, Masashi Hasegawa, Kozina Xeniya, Eiji Ikenaga

Journal of Alloys and Compounds 643 巻頁： 195-200 2015年

Growth of rectangular hollow tube crystals with rutile-type structure in supercritical fluids 査読有り

K. Niwa, H. Ikegaya, T. Taguchi, S. Muto, T. Tokunaga and M. Hasegawa

Journal of Physics: Conference Series (JPCS) 500 巻頁： 022007 2014年

High pressure synthesis of marcasite-type rhodium pernitride 査読有り国際共著

K. Niwa, D. Dzivenko, K. Suzuki, R. Riedel, I. Troyan, M. Eremets and M. Hasegawa

Inorganic Chemistry 53 巻頁： 697-699 2014年

レーザー加熱式ダイアモンドアンビルセルを用いた新物質合成招待有り査読有り

丹羽健，長谷川正

高圧力の科学と技術 24 巻頁： 178-187 2014年

Discovery of the last remaining binary platinum group pernitride RuN2 査読有り

K. Niwa, K. Suzuki, S. Muto, K. Tatsumi, K. Soda, T. Kikegawa and M. Hasegawa

Chemistry-A European Journal 20 巻 ( 43 ) 頁： 13885 - 13888 2014年

Argon Solubility in SiO2 Melt under High Pressures : A New Experimental Result using Laser-Heated Diamond-Anvil Cell 査読有り

K. Niwa, C. Miyakawa, J. Matsuda, T. Yagi

Earth and Planetary Science Letters 363 巻頁： 1-8 2013年

Characterization of Nb Hydrides Synthesized in High-Pressure Supercritical Water by Micro-beam Hard X-ray Photoelectron Spectroscopy 査読有り

K. Soda, H. Kondo, M. Kato, T. Shiraki, K. Niwa, K. Kusaba, M. Hasegawa, E. Ikenaga

Journal of Electron Spectroscopy and Related Phenomena 186 巻頁： 54-57 2013年

Pressure-induced noble gas insertion into zeolite LTA and its incompressible behaviors at high pressure 査読有り

K. Niwa, T. Tanaka, M. Hasegawa, T. Okada, T. Yagi, K. Kikegawa

MICROPOROUS AND MESOPOROUS MATERIALS 182 巻頁： 191-197 2013年

Effects of Sn2+ Ion Size on Sn Doped SrTiO3 査読有り

S. Suzuki, A. Honda, K. Suzuki, S. Higai, A. Ando, K. Niwa, M. Hasegawa

Japanese Journal of Applied Physics 52 巻頁： 09KC04 2013年

In-situ observation of shear stress-induced perovskite to post-perovskite phase transition in CaIrO3 and the development of its deformation texture in a diamond-anvil cell up to 30 GPa 査読有り

K. Niwa, N. Miyajima, Y. Seto, K. Ohgushi, H. Gotou, T. Yagi

Physics of the Earth and Planetary Interiors 194-195 巻頁： 10–17 2012年

High pressure induced water penetration into 3-isopropylmalate dehydrogenase 査読有り

T. Nagae, T. Kawamura, L. Chavas, K. Niwa, M. Hasegawa, C. Kato, N. Watanabe

Acta Crystallographica D 68 巻頁： 300–309 2012年

B1-to-B2 Structural Transitions in Rock Salt Intergrowth Structures 査読有り

T. Yamamoto, Y. Kobayashi, T. Okada, T. Yagi, T. Kawakami, C. Tassel, S. Kawasaki, N. Abe, K. Niwa, T. Kikegawa, N. Hirao, M. Takano, H. Kageyama

Inorg. Chem. 50 巻頁： 11787-11794 2011年10月

Growth and optical properties of rectangular hollow tube TiO2 crystals with rutile-type structure 査読有り

K. Niwa, T. Taguchi, T. Tokunaga, M. Hasegawa

Crystal Growth & Design 11 巻 ( 10 ) 頁： 4427-4432 2011年8月

Compression behaviors of binary skutterudite CoP3 in noble gases up to 40 GPa at room temperature 査読有り

K. Niwa, D. Nomichi, M. Hasegawa, T. Okada, T. Yagi, T. Kikegawa

Inorganic Chemistry 50 巻頁： 3281–3285 2011年3月

超高圧超高温下での超臨界流体を用いた無機化合物の合成と単結晶育成

長谷川正，丹羽健

セラミックス 46 巻頁： 378-385 2011年

ダイアモンドアンビルセルとレーザー加熱を用いた超高圧超高温超臨界流体中での結晶成長

長谷川正，丹羽健

日本結晶成長学会誌 38 巻頁： 4-11 2011年

Lattice-preferred orientations in post-perovskite-type MgGeO3 formed by transformations from different pre-phases 査読有り

T. Okada, T. Yagia, K. Niwa, T. Kikegawa

Phys. Earth Planet. Int. 180 巻 ( 3-4 ) 頁： 195-202 2010年6月

Submicron rectangular hollow tube crystals of rutile-type GeO2 査読有り

K. Niwa, H. Ikegaya, M. Hasegawa, T. Ohsuna, T. Yagi

J. Crystal Growth 312 巻 ( 10 ) 頁： 1731-1735 2010年5月

Deformation microtextures in CaIrO3 post-perovskite under high stress conditions using a laser-heated diamond anvil cell 査読有り

N Miyajima, K Niwa, F Heidelbach, T Yagi and K Ohgushi

Journal of Physics: Conference Series 215 巻頁： 012097 2010年

Elasticity of CaIrO3 with perovskite and post-perovskite structure 査読有り

K. Niwa, T. Yagi, K. Ohgushi

Phys. Chem. Minerals 頁： DOI: 10.1007/s00269-010-0378-z 2010年

Decomposition of perovskite FeTiO3 into wustite Fe1-xTi0.5xO and orthorhombic FeTi3O7 at high pressure 査読有り

D. Nishio-Hamane, T. Yagi, M. Ohshiro, K. Niwa, T. Okada, Y. Seto

Physical Review B 82 巻頁： 092103 2010年

Combining FIB milling and conventional Argon ion milling techniques to prepare high-quality site-specific TEM samples for quantitative EELS analysis of oxygen in molten iron 査読有り

N. Miyajima, C. Holzapfel, Y. Asahara, L. Dubrovinsky, D.J. Frost, D.C. Rubie, M. Drechsler, K. Niwa, M. Ichihara, T. Yagi

J. Microsc. 238 巻 ( 3 ) 頁： 200-209 2009年6月

The stability and equation of state for the cotunnite phase of TiO2 up to 70 GPa 査読有り

D. Nishio-Hamane, A. Shimizu, R. Nakahira, K. Niwa, A. Sano-Furukawa, T. Okada, T. Yagi, T. Kikegawa

Phys. Chem. Minerals 37 巻 ( 3 ) 頁： 129-136 2009年3月

Synthesis of Ln nitrides (Ln = Ce, Pr, Gd, Lu) in high pressure and temperature 査読有り

K. Niwa, M. Hasegawa, T. Yagi

J. Alloys Compd. 477 巻頁： 493–497 2009年

A new high-pressure polymorph of Ti2O3: implication for high-pressure phase transition in sesquioxide 査読有り

D. Nishio-Hamane, M. Katagiri, K. Niwa, A. Sano-Furukawa, T. Okada, T. Yagi

High Pressure Research 29 巻頁： 379-388 2009年

高圧下におけるSiO2メルトへの希ガス溶解度査読有り

丹羽健，八木健彦，宮川千絵，松田准一

高圧力の科学と技術 18 巻頁： 44-54 2008年

DACを用いたMgGeO3ポストペロブスカイト相の塑性変形実験と選択配向の観察査読有り

岡田卓，八木健彦，丹羽健

高圧力の科学と技術 18 巻頁： 244-253 2008年

Lattice Preferred Orientation in CaIrO3 Perovskite and Post-Perovskite Formed by the Plastic Deformation Under Pressure 査読有り

K. Niwa, T. Yagi, K. Ohgushi, S. Merkel, N. Miyajima, T. Kikegawa

Phys. Chem. Minerals 34 巻頁： 679-686 2007年

Synthesis of new La nitrides at high pressure and temperature 査読有り

M. Hasegawa, K. Niwa, T. Yagi

Solid State Commun. 141 巻頁： 267-272 2007年

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